A hydraulic system of this type for use in a motor vehicle brake system is known, for example, from DE 10 2005 028 562 A1, which is incorporated by reference, wherein the pulsation damping means have differing configurations. Although the object is achieved in principle by this measure, the pulsation behavior continues to be capable of improvement. For example, the noise insulation in the interior of modern motor vehicles is optimized to such an extent that, for example, haptic feedback—such as, in particular, brake pedal vibration—intrudes especially negatively and is found objectionable.
Pulsation damping measures which are known in principle suffer from the disadvantage that they operate satisfactorily only at certain points.
ABS control interventions often take place at a braking pressure initiated by the driver of, for example, 100 bar and more and require a return delivery in the direction of the actuation unit THZ. Other interventions, such as the hydraulic operation of parking brake functions, require accelerated filling of brake calipers of comparatively large volume capacity, and therefore high volume flow with a comparatively low pressure level.
On the other hand, an optimized dosing capability combined with the highest possible NVH (Noise, Vibration and Harshness) comfort is demanded for assistance functions, which consequently require comparatively shallow pressure rise and/or pressure drop gradients in order to offer the highest possible comfort.
With regard to the volume flow delivery rate, the motor vehicle brake system is designed in principle in such a manner that the delivery capacity of the pump is dimensioned according to the maximum volume flow delivery required to cover especially safety-critical control interventions, such as stability control interventions (ESP), Anti-Rollover Protection (ARP) or the like. These interventions are based in principle on an autonomous system intervention without the ability to call on any support or prefilling by the vehicle driver. These marginal conditions require a comparatively large displacement volume (large piston diameter, long displacement stroke). This dimensioning has a negative effect in a pulsation evaluation and on noise behavior, especially when comparatively small delivery volumes are called for.
Furthermore, multi-circuit pumps predominantly have a jointly bundled drive train, so that all the pistons are constantly entrained during operation of the pump, even if no delivery flow is called for in any one of the pump circuits.
For example, if a delivery volume is withdrawn by the load from only one of two pump circuits, and if no delivery volume (zero delivery) is withdrawn from the other pump circuit, a negative pressure is formed (cavitation) in at least a part of the suction path of the pump circuit with zero delivery as a result of “suction throttled” operation. This is because the suction path of the pump is continuously closed. The negative pressure can liberate separated gas portions, leading to undesired compressibilities in the brake system.